Reference : Vibrational properties of LaNiO3 films in the ultrathin regime
Scientific journals : Other
Physical, chemical, mathematical & earth Sciences : Physics
Physics and Materials Science
Vibrational properties of LaNiO3 films in the ultrathin regime
Schober, Alexander [> >]
Fowlie, Jennifer [> >]
Guennou, Mael mailto [University of Luxembourg > Faculty of Science, Technology and Medicine (FSTM) > Department of Physics and Materials Science (DPHYMS)]
Weber, Mads C. [> >]
Zhao, Hongjian [> >]
Iñiguez, Jorge mailto [University of Luxembourg > Faculty of Science, Technology and Communication (FSTC) >]
Gibert, Marta [> >]
Triscone, Jean-Marc [> >]
Kreisel, Jens mailto [University of Luxembourg > CRC > Vice-rectorate for Research (VR Research)]
American Institute of Physics Publising LLC
[en] Collective rotations and tilts of oxygen polyhedra play a crucial role in the physical properties of complex oxides such as magnetism and conductivity. Such rotations can be tuned by preparing thin films in which dimensionality, strain, and interface effects come into play. However, little is known of the tilt and rotational distortions in films a few unit cells thick including the question of if coherent tilt patterns survive at all in this ultrathin limit. Here, a series of films of perovskite LaNiO3 is studied and it is shown that the phonon mode related to oxygen octahedral tilts can be followed by Raman spectroscopy down to a film thickness of three pseudocubic perovskite unit cells (similar to 1.2 nm). To push the limits of resolution to the ultrathin regime, a statistical analysis method is introduced to separate the Raman signals of the film and substrate. Most interestingly, these analyses reveal a pronounced hardening of the tilt vibrational mode in the thinnest films. A comparison between the experimental results, first principles simulations of the atomic structure, and the standing wave model, which accounts for size effects on the phononic properties, reveals that in the ultrathin regime, the Raman spectra are a hybrid entity of both the bulk and surface phononic behavior. These results showcase Raman spectroscopy as a powerful tool to probe the behavior of perovskite films down to the ultrathin limit.
Fonds National de la Recherche - FnR
CO-FERMAT FNR/P12/4853155/Kreisel and AFR, Grant No. 7749159.

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